In order to increase the recording capacity of an optical disk, it is necessary to reduce the wavelength of laser light which is required for data read/write. In currently prevalent DVD players or recorders, red semiconductor lasers having a wavelength band of 660 nm are widely used. Such a red semiconductor laser is produced, for example, epitaxially growing an InGaAlP-type compound semiconductor on a GaAs substrate.
In recent years, vigorous development efforts are directed to next-generation optical disks, in order to realize an increased recording capacity over that of the DVD. A light source for such a next-generation optical disk will be required to stably emit blue-violet laser light (wavelength band 400 nm), whose wavelength is even shorter than that of red light. A GaN-type semiconductor laser of the wavelength band of 400 nm is considered as a most promising light source for the recording/reproduction of next-generation optical disks such as the Blu-ray Disc (trademark).
Patent Document 1 discloses a semiconductor laser device which is suitably used as a short wavelength light source in an optical disk apparatus.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2003-59087